feat(ci): separate CI workflows by tooling with label-based execution

[Copilot]

Description

Implements label-based CI execution to prevent code-conversion and model-converter tests from running when working on data-migrator, and vice versa.

Label behavior on PRs:

• No labels → runs data-migrator CI (distro + e2e + integration tests)
• ci:data-migrator → explicitly runs data-migrator CI
• ci:model-converter → runs model-converter tests only
• ci:code-conversion → runs code-conversion tests only
• Existing scope labels (ci:runtime, ci:history, ci:identity) continue to control integration test subsets

Unconditional execution:

• Push to main, scheduled runs, and manual dispatch run all jobs regardless of labels

Implementation:

• Added if conditions to all CI jobs using GitHub Actions label expressions
• Data-migrator jobs default to running when no tooling labels present
• Tooling-specific jobs (model-converter, code-conversion) only run with explicit labels on PRs
• Documented label usage in README contributing section

Type of Change

• New feature (non-breaking change which adds functionality)
• Documentation update

Testing Checklist

Black-Box Testing Requirements

• Tests follow black-box testing approach: verify behavior through observable outputs (logs, C8 API queries, real-world skip scenarios)
• Tests DO NOT access implementation details (DbClient, IdKeyMapper, ..impl.. packages except logging constants)
• Architecture tests pass (ArchitectureTest validates these rules)

Test Coverage

• Added tests for new functionality
• Updated tests for modified functionality
• All tests pass locally

Architecture Compliance

N/A - CI workflow changes only

Documentation

• Updated README if user-facing changes

Checklist

• Code follows project style guidelines
• Self-reviewed the code
• Added comments for complex logic
• No new compiler warnings
• Dependent changes have been merged

Related Issues

related to #issue

Original prompt

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This section details on the original issue you should resolve

<issue_title>Separate CI for different tooling</issue_title>
<issue_description>### Acceptance Criteria (Required on creation)
Exclude the code-conversion and diagram-migrator CI from the Data Migrator CI

Hints

By default run the data-migrator CI
Based on PR labels CI runs for a single or multiple tooling

Links

Breakdown

Pull Requests

Dev2QA handover

• Does this ticket need a QA test, and are the testing goals not clear from the description? Add a Dev2QA handover comment
  </issue_description>

<agent_instructions>The GitHub action CI only runs the respective tests of its module. You can use the maven flag -f to specify the respective pom.xml, but am also open to better approaches.

• CI / model-converter
  • Only runs tests in module model-converter.
• CI / code-conversion
  • Only runs tests in module code-conversion.
• CI / distro
  • Only runs unit tests in module data-migrator.
  • No integration tests in data-migrator/qa/e2e-tests.
• CI / e2e
  • Only runs tests in module data-migrator/qa/e2e-tests.
• CI / it-history-h2
  • Only runs tests in module data-migrator/qa/integration-tests.
• CI / it-history-h2-windows
  • Only runs tests in module data-migrator/qa/integration-tests.
• CI / it-history-oracle
  • Only runs tests in module data-migrator/qa/integration-tests.
• CI / it-history-postgresql
  • Only runs tests in module data-migrator/qa/integration-tests.
• CI / it-identity-h2
  • Only runs tests in module data-migrator/qa/integration-tests.
• CI / it-identity-oracle
  • Only runs tests in module data-migrator/qa/integration-tests.
• CI / it-identity-postgresql
  • Only runs tests in module data-migrator/qa/integration-tests.
• CI / it-runtime-h2
  • Only runs tests in module data-migrator/qa/integration-tests.
• CI / it-runtime-oracle
  • Only runs tests in module data-migrator/qa/integration-tests.
• CI / it-runtime-postgresql
  • Only runs tests in module data-migrator/qa/integration-tests.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes Separate CI for different tooling #627

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